Lecture 7 - LGOs Ligand Group Orbitals LGOs b u σ 1 b g 1...

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1 Chem 172 Advanced Inorganic Chemistry Lecture 7 Molecular Orbital Theory Continue lecture 6 and simple polyatomic molecules Polyatomic Molecules Molecular orbital theory can be used to describe electronic structure of systems of multiple atoms from 3 to infinite number of atoms (solid), in a way very similar to diatomic molecules. ± MOs are formed by linear combination of AOs of same symmetry. ± The degree of interaction depending on the relative energy match between AOs and distance (interaction between non- nearest neighbor are weaker than nearest neighbors). ± N AOs combine to form N MOs. Ligand Group Orbitals AXn Ligand group orbitals: collection of matching orbitals on ligand (X) atoms. In AX2, group orbitals are the same combination that formed bonding and antibonding orbitals in diatomic molecules, but they are now separated by the central atom and at larger distance with weaker interaction. Example: FHF - Example: FHF - Ligand Group Orbitals
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Unformatted text preview: LGOs Ligand Group Orbitals LGOs b u σ 1 b g 1 u π 1 * 2 g * 2 u Example: BeH 2 2 x z y Walsh Diagram for AH 2 90° 180° ∠ HAH 2a 1 2 σ g 1 σ u 3a 1 1b 2 1b 1 1 π u + + + + + + + + +-+-+ + +-+-+-A diagram that shows how one set of obitals evolve into another when one parameter (e.g. H-A-H angle) changes. OH 2 H H LGO 2p z 2p x 2p y 2s O 1s O H H x z y O H H Summary: How to Draw Molecular Orbital Diagram 1. Plot atomic valence orbital energies (or fragment orbitals for more complex molecules) . 2. Determine which orbitals can interact (symmetry match). 3. Determine magnitude of each interaction: scales directly with magnitude of overlap scales inversely with orbital energy difference 4. Plot MO energies and draw orbitals (nAOs → nMOs) Interaction Æ bonding + antibonding None Æ no change 5. Use Aufbau principle to fill in electrons Next Lecture Acid-Base Reading MT Chapter 6...
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This note was uploaded on 06/27/2010 for the course CHEMISTRY Chem 172 taught by Professor Duan,x. during the Spring '10 term at UCLA.

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Lecture 7 - LGOs Ligand Group Orbitals LGOs b u σ 1 b g 1...

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